As modern aircraft have become increasingly complex, aircraft flight controls have made increasing use of computer systems to organize and simplify the pilot's workload. Accordingly, modern aircraft include computer keyboards, cursor control devices, displays and other input/output devices that accept commands and data entered by the pilots and display this information to the pilots. For example, FIG. 1A illustrates a conventional control display unit (CDU) 30 having input devices 31 (e.g., keyboard keys) and a display screen 35 for displaying data. The display screen 35 can include a preview field 32 that displays information as the pilot enters keystrokes with the input devices 31. For example, in response to a system request to input an airport identifier, the pilot has entered the character string “X34A,” which appears in the preview field 32 shown in FIG. 1A.
When the pilot's entry is erroneous (as it is in FIG. 1A, because an airport identifier should not include any numbers), the pilot is notified in a manner shown in FIG. 1B. In particular, the pilot's entry at the preview field 32 is overwritten by the text “INVALID ENTRY.” Overwriting the pilot's entry with a short message is necessitated by the fact that space available for pilot displays (and in particular, the space available at the display screen 35 of the CDU 30) is extremely limited. However, this approach suffers from at least two drawbacks. First, once the message “INVALID ENTRY” is displayed, the pilot can no longer see the input that prompted the error message. Accordingly, the pilot cannot review the input to determine what prompted the error message. Second, while the error message makes clear that the pilot made an invalid entry, it does not provide the pilot with any guidance for correcting the error. Accordingly, the pilot's attempts to correct the error may be conducted by trial and error, which can be time consuming.